1. Field of the Invention
The present invention relates to access plugs for sealing inspection ports or insulated vessels or pipes in chemical processing facilities and the like.
2. Description of the Related Art
Chemical processing equipment containers or walls conventionally have been enclosed within an insulative covering of foam or similar material. Periodically, it has been required to monitor or test the container walls or equipment for safety or environmental reasons. Access ports or passages have thus been formed in the insulative covering so that test instrumentation could gain access to the wall.
U.S. Pat. No. 5,351,718, of which applicant is inventor, provides an access plug flange assembly suitable for being fitted into an insulative covering on chemical processing equipment. Access plug flanges of this type have proven suitable for a considerable number of situations for chemical processing equipment insulative coverings.
U.S. Pat. No. 5,520,220, of which applicant is also inventor, provides an access mounting flange assembly suited for insulation coverings on cold temperature chemical process equipment. These types of access mounting flanges have addressed problems encountered with relatively cold chemical processing applications, such as protecting the integrity of a vapor barrier in the equipment insulation.
So far as is known, however, when the processing equipment was at high temperatures (typically at about 450.degree. F. or higher) or when superheated steam was in the containers or vessels, additional problems have been encountered.
At temperature levels in this range, the silicone rubber in the sealing plugs or other components experienced problems. Oils present in the silicone elastomer materials leached out due to the high temperatures, causing the silicone seal to shrink and harden. This has caused the seal to lose its sealing ability, and in some cases fall out of its mounting. One proposal to remedy this problem was to add additional loose insulative padding. However, this loose insulation was often discarded or lost by the service crews when inspection service checks were performed. Also, some plug designs with metal caps and elastomer rings became difficult to remove due to both expansion of the metal cap and contraction of the rubber ring. In other designs, when adequate force was exerted to remove the plug, portions of the assembly, such as the metal expansion collar would also come out. This caused damage, often destroying the weather sealing effect.
So far as is known, the prior inspection port seals have been able to withstand only those temperatures that the silicone rubber components were capable of withstanding. The metal components of the flange had different thermal coefficients of expansion from those of the resilient materials in other parts of the flange provided to function as weather-tight seals. This has given rise to possible spaces or gaps in the seals, defeating their intended purpose.